Lymphodepleting chemotherapy potentiates neoantigen-directed T cell therapy by enhancing antigen presentation.

Adoptive cell therapy (ACT) targeting tumor-specific antigens holds promise for solid tumors, but limited neoantigen presentation remains a key barrier to efficacy. Here, we identify and characterize a T cell receptor (TCR), T104, for the KRAS.G12V mutation, a prevalent neoantigen in colorectal, lung, and pancreatic cancers. TCR-T104 selectively recognizes and kills KRAS.G12V-expressing tumor cells. Combining T cell therapy with lymphodepleting chemotherapy significantly enhances tumor cell killing, particularly by TCR-T cells, tumor-infiltrating lymphocytes (TILs), and T cell engager antibodies across multiple cancer types and target antigens. Mechanistically, chemotherapy upregulates immunoproteasome activity and human leukocyte antigen (HLA)-I surface expression. HLA-immunopeptidome analyses reveal that chemotherapy remodels the antigenic landscape across tumor cell lines and in vivo models, increasing peptide abundance and hydrophobicity while altering proteasomal cleavage preferences. These findings establish a synergistic role for chemotherapy in enhancing neoantigen presentation and T cell-mediated tumor recognition and suggest that fine-tuning these regimens could improve ACT efficacy, particularly in tumors with low-abundance neoantigens.